Printed circuit boards are used ubiquitously for a wide range of applications. A typical printed circuit board (or PCB) has a top and bottom surface, on which components may be affixed, such as by soldering. Between the top and bottom surfaces are a plurality of layers used to carry signals from one point on the PCB to another point. Each layer is comprised of an insulating material with conductive traces disposed thereon.
Signals can begin on one layer to move to another layer through the use of vias. Vias are conductive pathways that connect signals on various layers together. If the layers of the PCB are defined as being horizontal planes, these vias are typically vertical conductive pathways. In some embodiments, the vias pass through the entirety of the PCB. In other embodiments, known as blind vias, the via is accessible on either the top or bottom surface, but does not pass through the entirety of the PCB. In another embodiment, known as buried vias, the via may connect signals on two interior layers and not be accessible on either outer surface.
Vias have been used successfully for many years to carry signals between layers on printed circuit boards. However, as the frequencies of the signals on these PCBs continue to increase, vias have some limitations. For example, the high frequency signal may emit electromagnetic radiation to the interior layers through which it is passing. Furthermore, the impedance of the via may be different than the impedance of the signal traveling on a particular layer. This difference in impedance may cause undesirable reflections, affecting system performance.
In some implementations, it may be important to have PCBs which display high isolation and low cross talk. Furthermore, it may be important to have high dynamic frequency range electromagnetic transmission. Therefore, an improved PCB and a method of manufacturing such a PCB may be beneficial.